/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.jena.dboe.trans.bplustree.rewriter;

import java.util.Iterator;
import java.util.NoSuchElementException;

import org.apache.jena.atlas.iterator.PeekIterator;
import org.apache.jena.dboe.base.recordbuffer.RecordBufferPage;

/**
 * From a stream of RecordBufferPage, manage the link fields. That is, be a one
 * slot delay so that the "link" field can point to the next page. Be careful
 * about the last block.
 *
 */
class RecordBufferPageLinker implements Iterator<RecordBufferPage> {
    PeekIterator<RecordBufferPage> peekIter;

    RecordBufferPage               slot = null;

    RecordBufferPageLinker(Iterator<RecordBufferPage> iter) {
        if ( !iter.hasNext() ) {
            peekIter = null;
            return;
        }

        peekIter = new PeekIterator<>(iter);
    }

    @Override
    public boolean hasNext() {
        if ( slot != null )
            return true;

        if ( peekIter == null )
            return false;

        if ( !peekIter.hasNext() ) {
            peekIter = null;
            return false;
        }

        slot = peekIter.next();
        RecordBufferPage nextSlot = peekIter.peek();
        // If null, no slot ahead so no linkage field to set.
        if ( nextSlot != null )
            // Set the slot to the id of the next one
            slot.setLink(nextSlot.getId());
        return true;
    }

    @Override
    public RecordBufferPage next() {
        if ( !hasNext() )
            throw new NoSuchElementException();
        RecordBufferPage rbp = slot;
        slot = null;
        return rbp;
    }

    @Override
    public void remove() {
        throw new UnsupportedOperationException();
    }
}
